Contemporary battery charger systems often have provision for a variable charge rate that is selected depending on the charge state of a battery. Often, these battery chargers pro, vide a current to the battery at a high rate until the battery is mostly charged, and then provide another current at a low rate to top-off the charge. Typically, these rates are fixed and are not programmable.
With the continuous development of new battery technologies, methods for charging these batteries must also evolve to stay effective. A particularly important aspect of effectively charging a battery is not to exceed its maximum charging voltage and over-charge specifications. It is also important to ensure the maximum battery temperature is not exceeded during charging. The maximum charging voltage limit is the maximum threshold voltage at a battery's terminals. The over-charge specification can be defined in terms of the ratio of the total input charging energy to its battery capacity. In order not to exceed these specifications, it is advantageous for a battery charger to differentiate the type of battery being charged. Then, optimize its charging rates for that type of battery. For instance, Lithium batteries are particularly sensitive to threshold voltage during charging. If the threshold voltage is exceeded, it could cause the internal pressure of the battery to rise rapidly and eventually cause the battery to explode, which is a real safety hazard. Also, if a batten is charged exceeding its overcharging specification, then the useful cycle life as well as battery capacity can be reduced. Because of these adverse effects, devices used to charge batteries must not exceed these limits while quickly charging the battery.
As battery technologies evolve and the expectations of longer charging cycle life increase, these specifications continue to get increasingly intolerant. For example, with NICAD battery technology, the over-charge specification may be 120% of capacity. With newer Lithium based technologies, an over-charge above 100% of capacity is not recommended must be avoided. This requires a more resolute and higher accuracy charging system to efficiently charge these batteries.
Beneficially, newer battery technologies are emerging with a capability of providing a charge personality. This personality can be used by the charger to more efficiently charge these batteries. Now, the accuracy and resolution of providing charge current over a wide range, perhaps several decades of currents, is becoming vital. Conventional charging systems do not have the capability to provide the required accuracy and resolution over several decades.
What is needed is an improved variable charge rate battery charger with multiple range current control, especially when a variety of batteries are used with the sine charger. This apparatus must include the capability to provide charge current that is more accurate and has higher resolution current control over multiple current ranges.